1. Field of the Invention
The invention relates to a shield mounting method on a turbine casing of an engine structure, in particular a turbine mounted on an aircraft or a land industrial turbine, as well as a mounting assembly for implementing such a method.
2. Description of the Related Art
The field of the invention is more particularly the protection of engines, especially for power turbines, such as turbo-engines of aircrafts. The engine structure requires the presence of a protection shield to confine any part or element being able to break away from the engine structure or the casing. In particular, the shielding of a free turbine provides the retention of all free turbine blades upon an event of the “blade-shedding” type in case of overspeed. Indeed, the blades are built to break in a given speed range so as to guarantee the operation capacity of the engine under a given threshold and guarantee the integrity of the disks beyond such threshold.
Such a shield is in general embedded into the architecture of the engine casing and the adjacent parts. It can be limited to a solid portion. The shield is fastened to the casing through numerous assembling flanges or equivalent.
But it seems that the lifetime of such shielding flanges may be strongly limited. In particular, the differences in thermal inertia and stiffness between the flanges and the adjoining parts have an impact on the behavior of the parts in transition states, i.e. in power rise or drop.
According to another architecture, an internal shield running in a warm air is mounted between two casings. However, such an environment may limit the shield retaining capacities, which will then require more consequent thicknesses. Moreover, the presence of an external casing leads to a non negligible extra mass.
In such architectures, the efforts are directly transmitted to the engine structure. Such a transmission can lead to a progressive breaking away from the fasteners as well as shielding vibrations to the prejudice of the flight security.
Furthermore, there are shields fastened by screws arranged in high point by centering with pegs pointing at the screws. Such mounting requires precise and delicate adjustment to be implemented. Moreover, the lifetime of the pegs is random as regards vibratory transitions and other phenomena: “fretting”, shearing, etc.